SAN FRANCISCO -- Using glycated hemoglobin (HbA1c) to diagnose diabetes may miss more than half of cases, researchers reported here.

Action Points

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Note that this study of NHANES (a periodic U.S. national health study) demonstrated poor sensitivity of using hemogoblin A1c as a diagnostic test for diabetes mellitus.

Be aware that the authors have not yet reported the loss of specificity that might occur by using a cutoff A1c of 6.0%.

SAN FRANCISCO -- Using glycated hemoglobin (HbA1c) to diagnose diabetes may miss more than half of cases, researchers reported here.

In a review of national epidemiologic data, only about 43% of patients who met the criteria for diabetes based on fasting plasma glucose (FPG) were also diagnosed as diabetic using a typical HbA1c cutoff of 6.5%, Jinsun Choi, MD, of City of Hope National Medical Center in Duarte, Calif., and colleagues reported at the Endocrine Society meeting here.

"Based on this analysis, we can definitively say that the sensitivity of HbA1c of 6.5 is not very good; it's actually very low," Choi told MedPage Today.

Diagnosing diabetes has long been measured as having an FPG ≥126 mg/dL or having a 2-hour post-challenged plasma glucose ≥200 mg/dL in patient with classic symptoms of hyperglycemia. But a few years ago, the American Diabetes Association recommended including HbA1c ≥ 6.5% as another option for diagnosis of the condition.

However, controversy has swirled over whether or not to diagnose the disease this way, with some researchers have cautioning that using this cutoff could miss too many cases of diabetes.

So to examine the effectiveness of using HbA1c in diagnosing diabetes, Choi and colleagues assessed datasets from the National Health and Nutrition Examination Survey (NHANES), which totaled 5,764 patients who were at least age 18 and had documented blood sugar screening.

Overall, 245 of these patients (4.25%) met criteria for diabetes by FPG guidelines, but among them only 106 patients (43.27%) had an HbA1c ≥ 6.5% -- a fairly low sensitivity, the researchers said.

The specificity was better, at 99.28%, and the negative predictive value was 97.53% -- due to the low overall incidence of diabetes -- but the overall positive predictive value of the HbA1c test was only 72.60%, they reported.

To further analyze the data, Choi and colleagues categorized the patients by FPG values, either above or below 126 mg/dL, but found no consistent relationship.

"All the categories show no statistical significance," Choi said. "It tells me that we're unable to find any subgroup of patients in whom an HbA1c of 6.5% would not be a good measure to diagnose diabetes."

The researchers also looked for an equivalent HbA1c value with respect to FPG, but they found that HbA1c correlated with FPG very well (r=0.7058, P<0.000001). Based on this correlation, an FPG of 126 mg/dL correlated closer to an HbA1c ≥ 6%, they reported.

"If the FPG is 126, it actually correlates better with an HbA1 of 6.0% and not 6.5%," Choi said. "In fact, if you look at 6.5% HbA1c, the FPG would more be towards the 145 or 150 range."

She concluded that using an HbA1c ≥ 6.5% to diagnose diabetes will truly catch less than 50% of diabetic patients defined by FPG.

"In order to be consistent with diabetes diagnosed by FPG," she said, "we propose to use HbA1c ≥ 6.0% as a diagnostic criteria."

A co-author reported relationships with AstraZeneca and Bristol-Myers Squibb.

Reviewed by F. Perry Wilson, MD, MSCE Instructor of Medicine, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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